The disclosure relates to a sliding shoe for a hydrostatic axial piston machine of swash plate design.
In axial piston machines of swash plate design, a cylinder drum rotates together with a driving shaft. Axial cylinder bores and corresponding pistons are provided in the cylinder drum, in a uniform manner around the circumference. The pistons are coupled to a swash plate via their piston feet and via sliding shoes. As a result of the inclined position of the swash plate with respect to the rotation axis of the cylinder drum, the pistons execute a stroke movement out of the cylinder bore and a stroke movement into the cylinder bore upon each revolution of the cylinder drum. If the inclined position of the swash plate with respect to the cylinder drum is adjustable, the swept volume of the axial piston machine is adjustable.
The revolving sliding shoes have to be constantly held against the stationary swash plate and have in this case a sliding face by way of which they slide over the swash plate. Since the working pressure prevailing in the cylinder bores for a part of the revolving path thereof presses the sliding shoes in question against the swash plate, in order to minimize wear and to reduce frictional losses, hydrostatic relief means are provided in the sliding faces of the sliding shoes. Each sliding shoe has, on its sliding face, at least one flat relief recess, also known as a pressure pocket, for forming and defining a relieving pressure field. The relief force depends substantially on the size of the relief recess and the relief pressure prevailing therein. The relief pressure is tapped from the associated cylinder bore that is under working pressure and is transmitted to the relief recess via a duct in the piston and in the piston foot and via the ball joint and via a duct in the sliding shoe.
Since the comparatively low housing internal pressure of the axial piston machine prevails at the outer periphery of the sliding face, a pressure gradient arises between the relief recess and the outer periphery of the sliding face. In order to seal off the relief recess, the latter is surrounded by that part of the sliding face that bears against the swash plate.
In this case, various forms of relief recesses and corresponding forms of remaining sliding surfaces are known from the prior art, wherein said remaining sliding surfaces are often reduced to narrow webs. Furthermore, it is known practice to connect different spaced-apart relief recesses together via grooves.
UK 983,310 shows various sliding faces of a sliding shoe of a swash plate axial piston machine. Proceeding from the central mouth opening of the duct, various branched grooves have been introduced into the sliding face, said grooves forming the relief recesses.
DE 102 35 813 A1 and DE 196 01 721 C2 each show a sliding face of a sliding shoe of a swash plate axial piston machine, in which concentric relief recesses and corresponding concentric webs are provided. An inner circular relief recess and a concentric outer relief recess are connected together via at least one short radial duct which passes through a concentric web.
A disadvantage of the last-mentioned sliding shoes is that, during operation of the axial piston machine in question, they tend toward material displacements and smearing.